Is any water good water? Clonal growth and reproduction differences in response to abiotic and biotic factors in vernal pools

Background/Question/Methods

            Intraspecific variation in response to biotic and abiotic factors may help explain observed patterns of species distribution in nature.  As part of a larger project examining eco-evolutionary feedbacks on colonization dynamics of zooplankton in newly formed pools, we tested clonal differences of Daphnia pulex in response to several variable pool conditions.

            In order to understand how vernal pools affect amphibian and invertebrate population size and diversity, over seventy vernal pools were constructed. in summer 2010.  This provided a unique opportunity to test the effects of abiotic (pool chemistry) and biotic (presence of specific predatory invertebrates) filters on zooplankton growth, reproduction and survival. Over the summers of 2010 and 2011 the pools were sampled on a bi-weekly basis for standard limnological data.

            In 2010, regional Daphnia pulex clones were collected and genotyped D. pulex was then stocked into the pools in early 2011 at low and high genetic diversity.  Clonal growth and reproduction differences under standard conditions and in response to (1) kairomones from Chaoborus americanus, (2) pond water from different ponds, and (3) variable trace nutrients -- Se, Mn and Zn at varying concentrations -- were tested in the laboratory.  Success in laboratory experiments was compared with success in the pools .

Results/Conclusions

            We found that both existing pools in the region and the recently constructed vernal pools have extremely high among pool variability in many parameters,including invertebrate composition, pH, dissolved oxygen (DO), conductivity, and temperature.  During the same sampling period temperature varies as much as 15 deg. ^oC, pH varies from 5.6 to 8.9, DO varies from hypoxic to saturated, conductivity varies from 8 to 481 us/cm, and many major nutrients and trace elements vary by several orders of magnitude among pools.  We have also measured significant clonal differences in the growth and reproduction of D. pulex, both under standard conditions and in response to karimones released by C. americanus.  We will use our additional laboratory assays to estimate the degree to which differential performance (growth, reproduction, abundance in the field) of D. pulex in the ponds is due to clonal difference in response to bulk water chemistry and variability in specific trace elements (Se, Mn and Zn).